Finish lead for electrical transformer



H. L. KING 3,543,296

FINISH LEAD FOR ELECTRICAL TRANSFORMER Nov. 24, 1970 Filed March 1, 1968 16' 52 PRIOR ARr I 3,543,206 FINISH LEAD FOR ELECTRICAL TRANSFORMER Harry L. King, deceased, late of Pittsburgh, Pa.; Ednamae D. King, administratrix of said Harry L. King, assignor to McGraw-Edison Company, Elgin, Ill., 21 corporation of Delaware Filed Mar. 1, 1968, Ser. No. 727,757 (Filed under Rule 47(b) and 35 U.S.C. 118) Int. Cl. H01j 15/10 US. Cl. 336192 7 Claims ABSTRACT OF THE DISCLOSURE A finish lead for a coil of a high voltage transformer. The conductors extending from the coil are separated to form the outer portion of the finish lead. Additional conductive material is then inserted between the separated conductors in electrical contact with them to complete the finish lead.

= This-invention relates to windings for electrical transformers and more particularly to finish leads for individual coils of such windings.-

It is desirable in electrical transformer design to eliminate the formation of corona on electrical conductors wherever possible. The ionization of air at irregularities on the surface areas of the energized parts of an electrical transformer results in the formation of corona at these irregularities, particularly at higher potentials. The solution to the design problem consists, in part, of avoiding roughsurfaces or sharp edges and points in the coils and coil connections of the transformer windings.

Another problem, in transformer design is the high thermal gradientbetfween the conductor surface and the outer surface of the insulation on the finish lead of the coils of the transformer windings. Increased insulation is required on the finish'zleads due to high voltage insulation tests and the proximity of the finish leads to uninsulated parts of the transformer. In order to increase the current carrying capacity and reduce the thermal gradient at the finish leads to an acceptable value it has been the common practice of the prior art to affix additional conductors to the outside edge of the finish lead. The adding of the additional conductors to the outside edge of the finish lead, however, creates a rough and uneven condition and presents a number of sharp edges along the edge of the finish lead upon which corona will form. The rough condition of the conductors added tothe outside edge of the finish lead may be eliminated only by a considerable amount of labor which adds to the cost of the transformer.

It is accordingly a principle object of this invention to provide an improved finish lead for a coil of an electrical transformer which eliminates surface irregularities and requires a minimal amount of labor to construct.

It is a further object of the invention to provide a finish lead for a coil of an electrical transformer having additional conductive material! connected to it and which presents no irregular surface areas.

It is a further object of the invention to provide a finish lead for a coil of an electrical transformer having additional conductive material inserted between the extended conductors of the coil and which requires a minimal amount of labor to eliminate rough surfaces and sharp edges on the finish lead.

The present invention accomplishes'the above stated objects by providing a finish lead for a coil in which the conductors of the coil are extended and separated and additional conductive material is inserted between the separated conductors. The coil conductors may be separated to form one space between them or each of the United States Patent ice conductors may be separated from adjacent conductors and a separate piece of conductive material may be inserted in each of the resulting spaces.

Other objects and advantages of the invention will in part be obvious and will in part appear hereinafter. For a a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a plan view showing a finish lead extending from the coil of an electrical power transformer;

FIG. 2 shows a finish lead illustrating a first embodiment of the invention;

FIG. 3 shows a finish lead illustrating a second embodiment of the invention;

FIG. 4 shows a finish lead illustrating a third embodiment of the invention; and

FIG. 5 shows a finish lead illustrative of structures known in the art.

With reference to FIG. 1, a pancake type electrical coil 2 is illustrated. A secondary (not shown) may be wound within the central opening 6. The coil 2 may be mounted along with other similar coils in a transformer casing (not shown) and has a leg of a magnetic core (not shown) extending through its central opening 6. The coil 2 is concentrically wound and has a finish lead 4 extending from its outer periphery 8. A terminal plate 10 may be attached to the finish lead 4. An insulation wrappings 12 is wound around the conductors of the coil 2 and the finish lead 4. The insulation wrapping 12 will normally be wound to a greater thickness on the finish lead 4 due to the positioning of the finish lead near uninsulated members of the transformer casing (not shown). The finish lead 4 is held in tight support against the coil 2 by tying tape 14.

In the embodiment of the invention illustrated in FIG.

2, the finish lead 4 is shown without the insulation wrapping 12. The finish lead 4 has its outer conductors 16 and 18 formed from the conductors 20 and 22 extending from the coil 2. The bend portions 24 and 26 are formed in the finish lead conductors 16 and 18 so that a space is created between the finish lead conductors 16 and 18. The bend portions 24 and 26 have respective inner ends 28 and 30 positioned adjacent the coil 2. The bend portions 24 and 28 also have respective outer ends 32 and 34 positionedadjacent the exterior ends 36 and 38 of the finish lead conductors 16 and 18. The additional conductor 40 is inserted in the space between the finish lead conductors 16 and 18 and is supported in electrical contact with the finish lead conductors 16 and 18 by any suitable means such as brazing. Prior to inserting the additional conductor 40 in the space between the finish lead conductors 16 and 18, the additional conductor 40 may be formed to fit tightly within the space. It should be understood that the additional conductor 40 may consist of a single piece of conductive material or of a plurality of conductors or groups of conductors. After the forming of the finish lead 4 is completed, the insulation wrapping 12 may be wound around the finish lead 4 and the terminal plate 10 may be aflixed to it.

A typical finish lead 42 known in the prior art is illusstrated in FIG. 5. The additional conductors 44 and 46 are bent to follow the bend portion 48 of the finish lead 42. The additional conductors 44 and 46 are stepped at their inner ends 50 and 52. The stepping of the additional conductors 44 and 46 causes the edges 54 and 56 to be presented at the inner ends '50 and 52. Irregularities such as edges 54 and 56 result in the formation of corona and its attendant problems. Unlike the finish lead 42, the finish lead of the invention surrounds the additional conductors so that no edges are presented upon which corona may form.

In the embodiment of the invention illustrated in FIG. 3, the elements of the finish lead 60 identical with those elements of the finish lead 4 shown in FIG. 2 are referred to by the same reference numerals with the addition of the prime designation. The finish lead conductors 16' and 18' are respectively formed from the coil conductors 20 and 22'. The additional conductor 62 is supported between and in electrical contact with the finish lead conductors 16' and 18 of finish lead 60. However, little or no forming of the additional conductor 62 prior to insertion between the finish lead conductors 16' and 18' is required. Thus, even the minimal amount of work required to form the additional conductor 62 of FIG. 2 is eliminated in this embodiment of the invention.

In the embodiment of the invention illustrated in FIG. 4, the elements of the finish lead 70 identical with those elements of finish lead 4 shown in FIG. 2 are referred to by the same reference numerals with the addition of the double prime designation. The conductors 72, 16" and 18" of the finish lead 70 are formed from the coil conductors 74, 20" and 22". The additional conductors 76 and 40" are supported between and in electrical contact with the finish lead conductors 72, 16" and 18". The embodiment shown in FIG. 4 is particularly useful where the coil contains more than two conductors and a wide finish lead with even current distribution is desired.

While three specific embodiments of the invention have been shown herein, it will be realized that many modifications thereof are feasible without departing from the spirit and scope of the invention. For example, virtually any number of conductors or groups of conductors may extend from the coil and be utilized in forming the finish leads. The separation of the finish lead conductors may take any of a wide variety of bend shapes. It is consequently intended in the appended claims to cover all such variations and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a coil for an electrical transformer, said coil having a finish lead extending therefrom which includes two conductors and an additional conductor, the improvement in said finish lead comprising:

a bend portion having an inner end adjacent said coil and being formed in at least one of the two conductors, said two conductors being spaced apart between their exterior ends and the inner end of said bend portion, whereby a space is defined between said two conductors;

- .and said additional conductor is positioned in said space in electrical conductive relationship with said two conductors.

2. The combination according to claim 1 wherein said two conductors are positioned in a parallel relationship between their exterior ends and said bend portion.

3. The combination according to claim 1 wherein:

said bend portion is formed in each of said two conductors and is substantially L-shaped;

and said additional conductor is shaped to conform to a portion of the space between the two conductors.

4. The combination according to claim 2 wherein said additional conductor is shaped to conform to the entire portion of the space between the two conductors.

'5. The method of forming a finish lead for a coil of an electrical transformer from two conductors of the coil and an additional conductor which comprises the steps of forming a coil with two conductors:

extending said two conductors from said coil;

separating said two conductors to define a space therebetween exteriorly of said coil;

supporting the additional conductor in said space; I

and electrically connecting the additional conductor to said two conductors.

6. The method offorming a finish lead as defined in claim 5 wherein:

the separating step is accomplished by bending said two conductors; and the steps of supporting the additional conductor and connecting it to the two'conductors are per-' formed by brazing the additional conductor to the v two conductors.

I 7. The method of forming a finish lead as defined in claim 5 including the step of aligning an'end of said ad ditional conductor with the ends of said two conductors.

References Cited UNITED STATES PATENTS 3,216,089 11/1965 Dettman 29-626 3,320,566 5/1967 'Lohman 336-192 FOREIGN PATENTS 8/1959 Canada. 

